1. Field of the Invention
The present invention relates generally to reinforcement of ducts such as fibrous glass ducts, and in one of its aspects, to a method and apparatus for terminating tie rod reinforcing wire to reinforce a duct.
2. Description of the Prior Art
Ducts, especially air ducts for air conditioning and heating systems, are frequently constructed of structurally weak material such as fiberglass covered with metallic foil. Structural support is provided to such ducts by passing a tie rod reinforcing wire through two opposing sides of a duct and terminating the ends of the wire on the outsides of the duct in a way that prevents the wire from being pulled back through the duct. To prevent tearing of the duct by the terminations of the tie rod reinforcing wire, it has become common practice to use a support washer on the outside of the duct on each of the two opposing sides and to extend the wire through both support washers so that the wire termination exerts force against the washers rather than the sides of the duct. A conventional support washer is constructed of sheet metal with some ribbing to give it additional structural strength.
A commonly used termination for tie rod reinforcing wires makes use of what is known as "the double bend method". The double bend method involves bending the portion of wire protruding beyond the outside of each support washer approximately 90.degree. so that the wire makes contact with the support washer and then making an approximately 180.degree. bend in the wire roughly an inch or two beyond the original bend. Many attempts have been made to improve on the double bend method of tie rod reinforcing wire termination. One method of terminating a tie rod reinforcing wire which is currently in practice involves the use of an internal pop rivet sleeve which is placed over the tie rod reinforcing wire with the head of the rivet facing away from the duct. The pop rivet is slipped through the support washer until its head rests on the washer. The support washer and side of the duct are then pressed in slightly so that a crimping tool can be used to crimp the sleeve into the wire, thus completing the termination. An alternative method is known as the "external pop rivet sleeve" method and is similar to the internal pop rivet sleeve method except the sleeve is slipped over the wire with the head of the sleeve facing the duct so that the sleeve remains outside the duct. The sleeve is more easily crimped using the external pop rivet sleeve method, but this method leaves a significant protrusion on the outside of the duct which can be bumped into, tearing clothing and skin or damaging the duct.
One other method of terminating tie rod reinforcing wire for ducts is the use of a cap washer. A cap washer has a spring steel or stainless steel locking insert for holding a wire. A wire is cut so that a short protrusion remains on the outside of each support washer. A cap washer is then pushed onto each end of the wire.
The original double bend method is somewhat awkward to perform and leaves a protruding wire. The double bend method also has the tendency to unbend during high pressure conditions. The pop rivet sleeve methods require a pop rivet sleeve in addition to the support washers. Furthermore, the crimp connections are often poorly made and have relatively poor tensile strength. Crimping the sleeve using the internal pop rivet sleeve method is difficult and requires the person installing the reinforcement to depress the washer into the duct wall. The external pop rivet sleeve method leaves a significant protrusion on the outside of the duct walls. The cap washer method requires a cap washer and is relatively expensive when compared to the other methods.